PROJECT SUMMARY Multiple lines of evidence demonstrate the importance of the peripheral nervous system in the control of organ function. For the lung, neural innervation plays a key role in breathing, pulmonary blood pressure, and the ability to sense and respond to aerosol inputs such as allergen. Sensory innervation of the lung originates from neurons in the vagal ganglia with axonal projections along the vagus (which means ?wandering? in Latin) nerve. The vagus nerve projects to multiple organs, including the trachea, lung, heart and intestine. Most studies on vagal sensory neurons have focused on adult animals, and little has been done to understand the development of target organ innervation. Vagal sensory neurons have distinct embryonic origins; jugular neurons are derived from neural crest while nodose neurons are derived from epibranchial placode. Because of the many targets of the vagal ganglia, neurons are specified to allow for the diverse functions of vagal sensory neurons. Increasing evidence shows that there are multiple subtypes of vagal sensory neurons. For example, there is heterogeneity in cell sizes, nerve conducting speed, embryonic origin, and gene expression. How the diversity of sensory neurons is established during development is not understood. Whether cells are specified before or after target organ innervation is a key question. A suggestion that developmental cues may bias the pattern of innervation comes from findings that the majority of lung innervating sensory neurons are from the nodose, while the trachea is mainly innervated by jugular sensory neurons. I aim to test the hypothesis that ?not all those who wander are lost?, and determine if vagal sensory neurons are specified prior to sending projections to target organs. To accomplish this, I will first characterize when vagal ganglia projections reach target organs such as the trachea and lung, and whether they follow cues from blood vessels or existing motor nerves (Aim 1). I will determine if heterogeneity exists among vagal sensory neurons prior to lung innervation, based on an analysis of single-cell transcriptome of embryonic vagal ganglia before and after target organ innervation (Aim 2). Specifically, I will determine the expression patterns of Trk receptors within jugular and nodose sensory neurons prior to and after lung innervation, and determine if vagal sensory neuron specification depends on neurotrophic ligand expression before or after organ innervation (Aim 2). This project will investigate the co-development of the trachea/lung and their innervating nerves, and uncover the foundational knowledge of how the neural control of organ function is established.